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Old 17 March 2012, 10:52   #21
xs 400's Avatar
Country: UK - England
Town: yeovil
Boat name: Lilly of lyme
Make: XS
Length: 4m +
Engine: 30hp Yamaha
Join Date: Jul 2011
Posts: 631
Originally Posted by 9D280 View Post
80w AC - that's about right for three 21W bulbs + an instrument / cabin light.

OK, just to check I'm reading this right:

You have two green wires from the socket go to under the flywheel and also to a box which also has a red wire that at present is just hanging, and one of those green wires has a spare socket connected to it?

If so, that red wire is your battery charge, and the green is "tacho send". To sanity check, put your meter on DC V on a scale 0-20V DC across the red & any non painted bolt on the head, you should get something higher than 13V DC (I forget the min voltage that is needed to actually charge the battery, but it is >12) If you then do the same with the green, you should get next to nothing on DCV, but something between 8-20V AC. Values wooly as your meter is calibrated for 50Hz, the alternator changes frequency with RPM... and I've no idea how your meter will handle the variable frequency.

The book makes sense if it's wired like that - add lights and the electricity will go for the path of least resistance - i.e the lights - so not a lot will be left to feed the rectifier etc. You could use a 3 core cable to the console (get a nice chunky 15A if you use domestic cable - keeps the losses down) then a couple of red bullets (blue wonlt fit the Yam bullets) from your local car parts store for the R & G cables, and a suitable eye to go under one of the head bolts - job done.

Another option as your engine doesn't need it to stay aive is a cheap small car battery. My boat has had a minimum spec £40 bought 'coz it was avaialble at nanoseconds notice near where I was at the time battery in the console. That way if you do go for bigger electrics (e.g VHF / Nav. lights / electric start) you are future proofed. Probably not much more expensive than the big Maplin Gel batts if you shop around.
hi just managed to get hold of multi meter...........on idle from the red i have 6v dc , increasing the revs probably to 1500/1700 reading goes to 10v dc. presume if i increase revs more voltage will increase.

from the green i seem to have 3v dc

is this enough to charge a battery?

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